1. Field of the Invention
This invention relates to the disposal of solid wastes, particularly solid organic wastes, and further relates to an economical process for the preparation of fuels from waste materials. More particularly, this invention relates to a method for thermally decomposing and carbonizing solid organic wastes.
2. Description of the Prior Art
Pyrolysis processes are known for chemically converting organic materials to other, useful chemical products. Aside from the pyrolysis of raw materials (such as coal) which have recognized value in their unconverted state, some consideration has been given more recently to chemically converting solid organic wastes. For example, see "Industrial Solid Wastes Management," pp. 356-406, the Proceedings of the National Industrial Solid Wastes Management Conference, jointly sponsored by the University of Houston and the Bureau of Solid Waste Management on Mar. 24-26, 1970. Furthermore, methods for the concurrent pyrolytic treatment of solid organic materials and mineral oils are known.
It has been proposed to pyrolytically decompose rubber and plastic wastes by feeding the wastes either directly or in the molten state to a pyrolysis reaction furnace and maintaining the wastes therein for a sufficient period of time to decompose the wastes. For example, U.S. Pat. No. 3,956,414 describes a method of converting solid, amorphous polyolefin material to a liquid oil product which comprises melting the polyolefin by heating with a petroleum hydrocarbon oil and thermally cracking the resulting melt at a temperature of about 250.degree. to 450.degree. C. Other variations of the pyrolytic decomposition process are described in U.S. Pat. Nos. 3,674,433; 3,823,223; 3,832,151; and 3,984,288. The chief disadvantage of this approach is the amount of time required for the process to generate useful products in that heating times in excess of three hours are often required to decompose the rubber and plastics.
U.S. Pat. No. 1,950,811 discloses a process for recovering oil and high-temperature coke from oil-bearing residues by carbonizing oil-bearing residues from the destructive hydrogenation of coal and mineral oils in conjunction with natural carbonizable solid materials such as coal, peat, sawdust, and the like. More specifically, a high-temperature coke is produced at temperatures within the range from about 900.degree. to 1000.degree. C. (1650.degree. to 1830.degree. F.). To be contrasted with the process of U.S. Pat. No. 1,950,811 is the process disclosed in U.S. Pat. No. 2,054,725 which comprises "distilling" at relatively low temperatures--temperatures not exceeding about 380.degree. to 400.degree. C. (715.degree. to 755.degree. F.)--a mixture of about equal parts by weight of oil and a finely divided solid carbonaceous material containing volatile hydrocarbons.
U.S. Pat. No. 2,412,879 describes a process for continuously coking heavy petroleum residual oils in a moving bed coking zone to produce vaporizable hydrocarbons and a soft, highly frangible coke which may be continuously removed from the coking zone. According to the U.S. Pat. No. 2,412,879 process, the coker feed oil is slurried with from 1 to 10 percent by weight of a cellulosic material such as sawdust and heated to a temperature of from about 800.degree. F. to 1100.degree. F. before being charged to the coking zone. The sawdust forms an adsorbent charcoal during heating which, when intermixed with the formed petroleum coke, renders the coke more easily removable from the coking drum. Thus, the U.S. Pat. No. 2,412,879 process may be characterized as producing a petroleum coke having a relatively small amount of cellulosic-derived char associated therewith. A similar "additive-type" process is disclosed in U.S. Pat. No. 1,864,687.
U.S. Pat. No. 3,909,364 discloses and claims a method for treating carbonizable waste selected from the class consisting of garbage and sanitary sludge cake wherein the carbonizable waste is dried and commingled with coal, the commingled mix is devolatized to produce a devolatilized char, the char is partially combusted to produce heated char, and the heated char is mixed with residual oil and coked in a fluidized bed to produce a solid fuel product and fluid by-products. The U.S. Pat. No. 3,909,364 method requires extensive equipment: dryers, devolatilizers, heat generators, and fluid cokers. Moreover, the process is further complicated by the need for conveying solids between the various processing zones.
Given the proliferation of used rubber tires, plastic and paper packaging materials, one-way plastic and paper containers, by-product and substandard polymers, and solid organic wastes generally, improved methods of recovering the hydrocarbon values contained therein are needed, particularly in view of the increasing scarcity of oil and natural gas. The potentially valuable hydrocarbons in such materials would be better utilized if an economically attractive method could be devised for transforming them into useful liquid, solid, and/or gaseous hydrocarbon products having utility as fuel or as petrochemical raw materials.